1. Field of the Invention
The present invention is directed to an internal voltage control method and apparatus in a semiconductor memory device and more particularly, to method and apparatus which reliably operate a volatile semiconductor memory and reduce current surges through internal circuits in the volatile semiconductor memory when entering, exiting, or operating in a power down mode.
2. Discussion of Related Art
It has long been a goal for semiconductor memory designers to design higher cell capacity and faster semiconductor memories that also consume less power. Since Dynamic Random Access Memories (DRAMs) have a smaller cell size than Static Random Access Memories (SRAMs) and thus offer more memory capacity for a given chip size than SRAMs, usage of DRAMs may be preferred in electronic devices having space limitations. However, DRAMs require constant refreshing and draw much more current than SRAMs. For use in a portable or mobile device, the smaller size advantage of DRAMs disappears if a larger battery is needed or if the battery requires constant recharging. As mobile devices are equipped with increased sophistication and functions, demand for increased memory capacity naturally is also increased. Therefore, low power DRAMs are very much in demand.
Various circuits have been designed to reduce DRAM power consumption. For example, when the DRAMs are not operating in active mode, the DRAMs are put in standby or power down modes in which less or minimal current is provided to refresh or hold DRAM data. U.S. Pat. No. 6,058,063 to Jang (the ""063 patent) discloses a circuit for operating memory devices during standby or power-down mode. An external clock enable signal (CKE) is used to signal power-down mode and cut off power to certain circuits such as input buffers. FIG. 1A shows a circuit described in the ""063 patent. A power down signal PBPUB derived from CKE goes from a low level to a high level to signal power down. PBPUB disconnects VCC by switching off Transistor 31 and pulls the output to ground by turning on Transistor 32. The disclosure of the ""063 patent is incorporated by reference herein.
Recently, several DRAM manufacturers made proposals to JEDEC (Joint Electron Device Engineering Council) to standardize the use of a deep power down (DPD) signal for controlling entry and exit to and from a DPD operation mode in DRAMs. Proposals have been made to use the DPD signal to power down DRAMs when they are not in use, thus reducing power consumption.
Protocols for signaling DPD entry and exit modes proposed to JEDEC are shown in FIGS. 1B and 1C. FIG. 1B shows the protocol for DPD entry mode, wherein the DRAM is entering a deep power down mode. As shown in FIG. 1B, a DPD entry mode is signaled when a clock enable (CKE) signal, chip select (CS) signal, write enable (WE) signal go low, and row and column address strobe (/RAS and /CAS) signals stay high, triggered by a low to high CLOCK signal. FIG. 1C signals DPD exit. As shown, DPD exit mode is signaled when clock enable (CKE) goes high, triggered by a low to high CLOCK signal. As shown, the other signals do not affect DPD exit. It is understood that the protocol shown in FIGS. 1B and 1C are merely illustrative and variations to the protocol can be used or adopted for purposes of signaling power down entry and exit. For example, any or all of the control signals such as WE and CAS can have signal levels reversed from that shown or may not even be used to trigger CKE. Any equivalent clock enable signal can serve as CKE to invoke DPD entry and exit.
The proposed use of DPD is to power down the DRAM when the DRAM is not in active usage. Thus, upon entry in DPD mode, the various internal power voltage generators for supplying voltages such as cell capacitor plate voltage, internal array power voltage, internal peripheral power voltage, reference power voltage, etc. to internal circuits of the DRAM are turned off. Also turned off are nearly all the input buffers of the DRAM, except an auxiliary input buffer which will be kept on to receive the DPD exit mode signal.
In implementing DPD entry and exit, a large amount of input buffers and internal voltage generators are turned on and off at substantially the same time. This causes a large amount of current surging through the DRAM. A large current surge causes severe strain on the battery generate heat and may render a circuit inoperable. Further, certain nodes in circuits turned off may be floating at unspecified voltages and if the circuits are not turned on properly, false triggering of internal circuitry of the DRAM may also occur.
Accordingly, a need exists for a device and method for implementing DPD entry and exit with minimal current surges. A need also exists for a method and device for preventing false triggering of circuits when the DRAM is operating during, entering or exiting DPD mode.
A semiconductor device is provided for controlling entry to and exit from a power down (DPD) mode of a semiconductor memory, comprising; a plurality of voltage generators for providing operating voltages to the semiconductor memory; a DPD controller for detecting a DPD condition and generating a DPD signal to control the application of the operating voltages to the semiconductor memory; and biasing circuitry for biasing a plurality of nodes of at least one of the plurality of voltage generators to at least one predetermined voltage potential to prevent false triggering of circuits upon entry/exit of DPD mode, wherein the plurality of voltage generators are turned off during DPD mode and turned on upon exit from DPD mode for providing operating voltages to internal circuitry of the semiconductor memory and a peripheral voltage generator for providing a peripheral voltage to a peripheral circuit; the biasing circuitry further including a peripheral voltage control circuit for biasing the peripheral voltage to a known potential which is different than operating voltages of the internal circuitry.
Preferably, the bias potentials of the operating voltages to the internal circuitry during DPD mode is substantially at ground and the bias potential of the peripheral voltage is closer to bias voltage of the peripheral voltage control circuit. The peripheral voltage control circuit includes an output node and a bias node and at least one transistor for switching the output node to connect to the bias node through a diode during DPD mode. The semiconductor memory device is a DRAM.
A semiconductor device is also provided which comprises: a plurality of input buffers for buffering a plurality of DPD-type signals for signaling a power down (DPD) condition including a DPD enter/exit signal; an auxiliary buffer for separately buffering the DPD enter/exit signal; a plurality of voltage generators for supplying operating voltages to internal circuit; DPD control circuit for receiving the DPD-type signals to decode DPD enter and exit commands and for outputting a voltage generator control signal to turn off the voltage generators when DPD enter command is decoded, and to turn off the plurality of buffers excluding the auxiliary buffer; and an auto-pulse generator for generating a voltage pulse upon receiving the DPD exit command to initialize the internal circuit. The auto-pulse generator includes a two-input logic gate for receiving directly at one of the two inputs a DPD exit signal and receiving at the other of the two inputs a delayed version of the DPD exit signal.
According to one aspect of the present invention, a power voltage detector is provided for detecting the voltage output of at least one of the plurality of voltage generators for determining whether the one voltage generator is operating in power down mode; and an interlock circuit for receiving as inputs the DPD enter/exit signal and the output of the power voltage detector, and for outputting a DPD exit signal when the DPD enter/exit command signals a DPD exit mode and the one voltage generator outputs a voltage substantially at ground. The interlock circuit includes cross-coupled logic gates for blocking the output of the DPD enter/exit signal when the one voltage generator outputs a voltage other than substantially at ground.
A method is also provided for controlling entry to and exit from a power down (DPD) mode of a semiconductor memory, comprising; providing operating voltages to a plurality of voltage generators; detecting a DPD condition and generating a DPD signal to control the application of the operating voltages to the semiconductor memory, wherein the plurality of voltage generators are turned off during DPD mode and turned on upon exit from DPD mode for providing operating voltages to internal circuitry of the semiconductor memory; and; biasing a plurality of nodes of at least one of the plurality of voltage generators to at least one predetermined voltage potential to maintain operation of the at least one of the plurality of voltage generators during DPD node.
According to another aspect of the invention, a device is provided for controlling entry to and exit from a power down (DPD) mode of a semiconductor memory comprising means for providing operating voltages to a plurality of voltage generators, means for detecting a DPD condition and generating a DPD signal to control the application of the operating voltages to the semiconductor memory, wherein the plurality of voltage generators are turned off during DPD mode and turned on upon exit from DPD mode for providing operating voltages to internal circuitry of the semiconductor memory, and means for biasing a plurality of nodes of at least one of the plurality of voltage generators to at least one predetermined voltage potential to mountain operation of the at least one of the plurality of voltage generators during DPD node.
According to still another aspect of the invention, a semiconductor device comprises a plurality of input buffers for buffering a plurality of DPD-type signals for signaling a power down (DPD) condition including a DPD enter/exit signal a plurality of voltage generators for supplying operating voltages to internal circuit, means for receiving the DPD-type signals to decode DPD enter and exit commands and for outputting a voltage generator control signal to turn off the voltage generators and the plurality of buffers when DPD enter command is decoded, and means for generating a voltage pulse upon receiving the DPD exit command, wherein the pulse is used to initialize the internal circuit.